Final answer:
The most common chemical agent used for crowd control is tear gas (CS gas), which is a non-lethal chemical weapon designed to temporarily incapacitate individuals by causing eye and respiratory irritation.
Step-by-step explanation:
The most common chemical irritating agent used for incapacitation and crowd control is CS gas, more commonly known as tear gas. CS is an abbreviation for 2-chlorobenzalmalononitrile, a compound that irritates the mucous membranes in the eyes, nose, mouth, and lungs, causing tearing, sneezing, coughing, difficulty breathing, pain in the eyes, and temporary blindness. With effects usually lasting for less than an hour after exposure, it is considered an "incapacitating" agent rather than a lethal one.
Due to its high volatility, CS gas can be quickly disseminated over large crowds, rendering it effective for dispersement. Armed forces and police units often use this agent for crowd control, but its usage is controversial because it can cause severe discomfort and has been associated with serious injuries and fatalities under certain circumstances. Moreover, exposure to high concentrations or prolonged contact can lead to more severe health problems.
In comparison, lethal chemical warfare agents, such as nerve agents or blister agents, are designed to cause significant bodily harm or death. These agents are prohibited from use in international conflicts by various treaties and laws.